In the related art, an active-matrix liquid crystal display device is known that is provided with a display unit including a plurality of source bus lines (video signal lines) and a plurality of gate bus lines (scanning signal lines). In such a liquid crystal display device, a gate driver (scanning signal line drive circuit) configured to drive the gate bus lines is often mounted at a periphery of a substrate constituting a liquid crystal panel, as an Integrated Circuit (IC) chip. However, in recent years, the number of such liquid crystal display devices is increasing that have adopted a configuration where the gate driver is formed directly on a TFT substrate. The TFT substrate is one of two glass substrates constituting the liquid crystal panel. Such a gate driver is referred to as a “monolithic gate driver” or the like.
A display unit of an active-matrix liquid crystal display device is provided with a plurality of source bus lines, a plurality of gate bus lines, and a plurality of pixel forming units provided in association with respective intersections between the plurality of source bus lines and the plurality of gate bus lines. The plurality of pixel forming units are arranged in a matrix to form a pixel array. Each of the pixel forming units includes a thin film transistor that includes a switching element with a gate terminal connected to a gate bus line routed through the corresponding intersection and a source terminal connected to a source bus line routed through the intersection, and a pixel capacity configured to hold a pixel voltage value, and the like. The active-matrix liquid crystal display device is also provided with the above-described gate driver and a source driver (video signal line drive circuit) configured to drive the source bus lines.
A video signal indicative of a pixel voltage value is transmitted through the source bus lines. However, each source bus line is unable to transmit video signals indicative of pixel voltage values for a plurality of rows at a time (at the same time). Thus, the video signals are sequentially written (charged) into the pixel capacities in the above-described pixel forming units arranged in a matrix, on a row-by-row basis. Thus, the gate driver is constituted of a shift register with a plurality of stages to allow the plurality of gate bus lines to be sequentially selected at predetermined time intervals. Then, active scan signals are sequentially output from each stage of the shift register to allow the video signals to be sequentially written into the pixel capacities on a row-by-row basis as described above.
A circuit constituting each of the stages of the shift register is referred herein to as a “unit circuit”. A sequential selection of each gate bus line starting with the first gate bus line and ending with the final gate bus line is simply referred to as a “scan”, and a stoppage of the scan after the first line and before the final line is referred to as a “scan interruption”.
In recent years, there has been a growing popularity of a liquid crystal display device integrated with a touch panel and a liquid crystal panel together. In such a liquid crystal display device, a processing on the touch panel (for example, a processing for detecting a touched position) needs to be executed while a scan is not performed. However, in the shift register of the related art provided in the liquid crystal display device, all of the stages are configured in a similar manner. Thus, after the first gate bus line is selected, the scan cannot be stopped until the final gate bus line is selected.
Thus, PTL 1 discloses an invention for a shift register, enabling a scan interruption, in which an unit circuit (in PTL 1, described as a “transfer circuit”) corresponding to a position where the scan is to be interrupted is configured to hold the potential of an input shift signal (shift pulse) for a long period.